SPECTROSCOPIC EVIDENCE FOR INTERMOLECULAR M-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-H-OR HYDROGEN-BONDING - INTERACTION OF WH(CO)(2)(NO)L(2) HYDRIDES WITH ACIDIC ALCOHOLS
Es. Shubina et al., SPECTROSCOPIC EVIDENCE FOR INTERMOLECULAR M-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-H-OR HYDROGEN-BONDING - INTERACTION OF WH(CO)(2)(NO)L(2) HYDRIDES WITH ACIDIC ALCOHOLS, Journal of the American Chemical Society, 118(5), 1996, pp. 1105-1112
Intermolecular hydrogen bonding of acidic alcohols (PhOH, (CF3)(2)CHOH
(HFIP), (CF3)(3)CHOH (PFTB)) to the hydride ligand of WH(CO)(2)(NO)L(
2) (L = PMe(3) (1), PEt(3) (2), P((OPr)-Pr-i)(3) (3), PPh(3) (4)) has
been observed and characterized by IR and NMR spectroscopy in hexane,
toluene-d(8), and CD2Cl2 solutions. The H-bonding is an equilibrium pr
ocess with medium -Delta H degrees of 4.1-6.9 kcal/mol; the enthalpy i
ncreases on going from 4 to 1, i.e., the strongest bonding is found fo
r the smallest and the most basic L = PMe(3). The value of -Delta H de
grees depends on the pK(a) of the proton donors, increasing as the aci
dity does (PhOH < HFIP < PFTB). The IR and NMR data suggest C-2v symme
try around tungsten in the ROH ... HW(CO)(2)(NO)L(2) adduct, with the
H ... H distance of 1.77 Angstrom (L = PMe(3)) estimated from the hydr
ide T-1 min relaxation time. The relevance of the hydrogen bonding to
the mechanism of protonation of metal hydrides is suggested.